1. Field of the Invention
The present invention relates to a plasma display panel (PDP), and more specifically to an alignment mark for assembling a plasma display panel.
2. Description of the Related Art
Recently, a variety of flat panel displays, including liquid crystal displays (LCDs) and plasma display panels (PDPs) have been intensively developed to replace cathode ray tube (CRT) displays. The PDP luminescent principle follows. Ultraviolet light is first produced from gas plasma and emitted to excite red (R), blue (B), and green (G) phosphors, then multifarious visible light is produced by mixing these three primary colors.
A conventional PDP fabrication comprises the following steps. The front substrate comprising the formation of transparent electrodes, bus electrodes, a dielectric layer, and a protective layer is fabricated. The rear substrate comprising the formation of address electrodes, rib barriers, and RBG phosphors is then fabricated. Finally, assembly of the PDP comprising alignment for a front and rear substrates to form a discharge space, vacuuming the discharge space, conducting mixed gas used to discharge into the discharge space until proper pressure, and detecting the luminescent stability in the discharge space is performed.
FIG. 1 is a cross section of a conventional plasma display panel. A front substrate structure 10 comprises a glass substrate 11 with a pair front electrodes 12, 14 installed in parallel thereon, a dielectric layer 16 covering the glass substrate 11 and the front electrodes 12, 14, and a protective layer 18 formed on the dielectric layer 16, wherein the front electrodes 12, 14 comprise transparent electrodes 12A, 14A and bus electrodes 12B, 14B respectively.
The transparent electrode may comprise Indium-Tin-Oxide (ITO), and the bus electrode may comprise a metal material, such as Cr—Cu alloy, to increase the conductivity of the front electrodes. A rear substrate structure 20 comprises a glass substrate 21 with a lengthwise address electrode 22 installed thereon, a dielectric layer 24 covering the lengthwise address electrode 22, rib barriers 25 disposed on the dielectric layer 24 and dividing the space above the dielectric layer 24 into a plurality of cells, such as a plurality of rectangular or hexagonal cells.
RBG Phosphors 26 coated on the sidewalls of the rib barriers 25 and the dielectric layer 24 to form three-primary-color luminescent cells. A pixel comprises R, B, and G luminescent cells adjacent to each other. The front electrodes 12, 14 are perpendicular to the address electrode 22.
For luminance efficiency and quality assurance, it is necessary that the electrodes 12, 14 on the front substrate are accurately aligned with the center of the luminescent cells divided by the rib barriers 25 on the rear substrate, and are perpendicular to the address electrode 22 on the rear substrate structure 20.
Therefore, alignment accuracy during assembly is important to PDP quality. In other words, if the front electrodes 12, 14 are shifted from the center of the luminescent cells on the rear substrate, it may reduce excitation efficiency of inert gas within the luminescent cells, decreasing luminance efficiency and affecting color uniformity.
For improving alignment accuracy, in general, alignment marks are additionally installed on the outside of the front and rear substrates respectively.